Helmets and defensive body armor are typical equipment utilized by militaries throughout the world. The effectiveness of such equipment is related to both its strength and weight. Preferably, the armor will be both strong and light. The lighter the armor is, the easier it is to carry. The stronger the armor is, the more potential it has to successfully defend against an attack. However, in order to increase the strength of the armor, it is typically necessary to increase at least the thickness and/or density of the armor. Unfortunately, this will also increase the net weight of the armor. And, if the weight is increased too much, the armor can actually become more of an encumbrance than assistance during battle.
In view of the foregoing, there is an ongoing desire for the military to utilize materials that are both lightweight and strong. Titanium is one material that has been found to provide desirable strength to weight ratios, as well as beneficial anticorrosion properties. Accordingly, militaries have started incorporating increased amounts of titanium in their equipment. However, as described below, titanium is not practical in traditional forms of manufacture, such as casting.
To provide the specific strength and weight ratios that are desired, titanium is typically alloyed with various other elements, such as iron, aluminum, vanadium, molybdenum, as well as various other elements. It is anticipated that ongoing research will continue to develop new and interesting combinations of elements to incorporate into titanium alloys, as well as processes for manufacturing the alloys.
As the demand for titanium increases, the availability of refined titanium alloys remains somewhat restricted and the manufacturers of products incorporating titanium often experience long wait times for the specific alloys that are desired. Naturally, this increases the relative cost of utilizing titanium alloys in military equipment.
Another problem experienced by military product suppliers utilizing titanium, is that titanium is very difficult to cast, particularly into thin-walled products like helmets and body armor because of titanium's high melting point, around 3000° F., and low fluidity (the ability of the metal to flow into a mold when molten). In addition, titanium is highly reactive and has a high chemical affinity when molten. This causes the titanium to react with the surface of the mold, contaminating the casting and thereby causing inferior mechanical properties of the resultant titanium product.
For example, the reaction of molten titanium with a mold material during casting will also create oxide contaminates, such as ‘alpha case’, on the surface of the titanium. Alpha case is extremely hard and brittle and renders the casting subject to brittle failure and less suitable for ballistic protection.
The contamination that occurs during casting of titanium also increases the impracticality of superheating the titanium above the molten state in order to enhance the fluidity of the titanium, to help fill thin-wall casting molds. In particular, superheating the titanium above molten temperatures creates risks of even more severe contamination during the casting.
Titanium's high melting point also makes it difficult to ensure that an entire mold will be filled before the titanium begins to freeze or solidify within the mold. This problem is even more pronounced when casting titanium into thin-walled molds, since it can be difficult to maintain the titanium at the relatively high melting point of around 3000° F., during the entire casting process. As a result, the titanium will often freeze within the mold before the entire mold is filled, thereby resulting in product imperfections and holes that are clearly unacceptable for military applications, such as for helmets, body armor and many other products.
In view of the foregoing, casting titanium is often overlooked as a viable method for producing thin, bullet resistant helmets and body armor.
In order to form helmets and other thin walled armor products out of titanium, some manufacturers have begun using manufacturing processes, other than casting, such as superplastic and stamping processes. However, these processes require the titanium to be prefabricated into specific configurations, such as thin uniform sheets, that are amenable to the superplastic formation. Unfortunately, this eliminates the practical use of much of the available titanium, such as scrap titanium and titanium sponge. The prefabrication requirements also increase the relative costs and wait times for the desired titanium alloys.